Study of multi-step hydrometallurgical methods to extract the valuable content of gold, silver and copper from waste printed circuit boards

• Waste computer printed circuit boards have been used in the experimental work.
• The two-step counter-current oxidative leaching procedure was used for Cu extraction.
• The two-step cross-current thioureation leaching procedure has presented good efficiency on Au and Ag recovery.
• Both copper and precious metals were recovered in their solid form by cementation with Zn powder.

In this work, hydrometallurgical methods like counter and cross current chemical leachings and cementation have been studied and applied for copper, gold and silver recovery from waste printed circuit boards. 1.7 M H2SO4 (98% wt./vol.), 17% (V/V) H2O2 (30 wt./vol%.), solid/liquid ratio of 15 g/L, room temperature, with a continuous stirring rate of 200 rpm for 1 h have been the optimal conditions for Cu dissolution by the two-step counter current leaching procedure. The cross current leaching procedure with thiourea as reagent and triferric ion as oxidizing agent in diluted acid sulfuric media were involved for the dissolution of gold and silver. About 90% of Au and 75% of Ag extraction yield were obtained in the first step with 20 g/L of thiourea, 6 g/L of ferric ion, 0.1 M of sulfuric acid with a vigorous agitation of 200 rpm of 1 h at ambient temperature. In the solutions purification step, high recovery rates of both Cu and precious metals have been achieved by applying cementation process with Zn powder. This procedure can be considered of interest and is under continuously development for a further application on a small hydrometallurgical pilot plant.